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Rollup merge of #70748 - ogoffart:enum-layout-optim2, r=eddyb

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Do not disable field reordering on enums with big discriminant

The field are always re-ordered to minimize padding, regardless of the
alignment of the discriminant

(spinoff from #70477)
This commit is contained in:
Dylan DPC 2020-04-05 06:44:44 +02:00 committed by GitHub
commit 630414db42
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2 changed files with 28 additions and 5 deletions
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8
src/librustc_middle/ty/layout.rs
View File

@ -285,11 +285,7 @@ impl<'tcx> LayoutCx<'tcx, TyCtxt<'tcx>> {
let mut inverse_memory_index: Vec<u32> = (0..fields.len() as u32).collect();
let mut optimize = !repr.inhibit_struct_field_reordering_opt();
if let StructKind::Prefixed(_, align) = kind {
optimize &= align.bytes() == 1;
}
let optimize = !repr.inhibit_struct_field_reordering_opt();
if optimize {
let end =
if let StructKind::MaybeUnsized = kind { fields.len() - 1 } else { fields.len() };
@ -307,6 +303,8 @@ impl<'tcx> LayoutCx<'tcx, TyCtxt<'tcx>> {
});
}
StructKind::Prefixed(..) => {
// Sort in ascending alignment so that the layout stay optimal
// regardless of the prefix
optimizing.sort_by_key(|&x| field_align(&fields[x as usize]));
}
}

25
src/test/ui/type-sizes.rs
View File

@ -37,6 +37,29 @@ enum ReorderedEnum {
B(u8, u16, u8),
}
enum ReorderedEnum2 {
A(u8, u32, u8),
B(u16, u8, u16, u8),
// 0x100 niche variants.
_00, _01, _02, _03, _04, _05, _06, _07, _08, _09, _0A, _0B, _0C, _0D, _0E, _0F,
_10, _11, _12, _13, _14, _15, _16, _17, _18, _19, _1A, _1B, _1C, _1D, _1E, _1F,
_20, _21, _22, _23, _24, _25, _26, _27, _28, _29, _2A, _2B, _2C, _2D, _2E, _2F,
_30, _31, _32, _33, _34, _35, _36, _37, _38, _39, _3A, _3B, _3C, _3D, _3E, _3F,
_40, _41, _42, _43, _44, _45, _46, _47, _48, _49, _4A, _4B, _4C, _4D, _4E, _4F,
_50, _51, _52, _53, _54, _55, _56, _57, _58, _59, _5A, _5B, _5C, _5D, _5E, _5F,
_60, _61, _62, _63, _64, _65, _66, _67, _68, _69, _6A, _6B, _6C, _6D, _6E, _6F,
_70, _71, _72, _73, _74, _75, _76, _77, _78, _79, _7A, _7B, _7C, _7D, _7E, _7F,
_80, _81, _82, _83, _84, _85, _86, _87, _88, _89, _8A, _8B, _8C, _8D, _8E, _8F,
_90, _91, _92, _93, _94, _95, _96, _97, _98, _99, _9A, _9B, _9C, _9D, _9E, _9F,
_A0, _A1, _A2, _A3, _A4, _A5, _A6, _A7, _A8, _A9, _AA, _AB, _AC, _AD, _AE, _AF,
_B0, _B1, _B2, _B3, _B4, _B5, _B6, _B7, _B8, _B9, _BA, _BB, _BC, _BD, _BE, _BF,
_C0, _C1, _C2, _C3, _C4, _C5, _C6, _C7, _C8, _C9, _CA, _CB, _CC, _CD, _CE, _CF,
_D0, _D1, _D2, _D3, _D4, _D5, _D6, _D7, _D8, _D9, _DA, _DB, _DC, _DD, _DE, _DF,
_E0, _E1, _E2, _E3, _E4, _E5, _E6, _E7, _E8, _E9, _EA, _EB, _EC, _ED, _EE, _EF,
_F0, _F1, _F2, _F3, _F4, _F5, _F6, _F7, _F8, _F9, _FA, _FB, _FC, _FD, _FE, _FF,
}
enum EnumEmpty {}
enum EnumSingle1 {
@ -104,6 +127,8 @@ pub fn main() {
assert_eq!(size_of::<e3>(), 4 as usize);
assert_eq!(size_of::<ReorderedStruct>(), 4);
assert_eq!(size_of::<ReorderedEnum>(), 6);
assert_eq!(size_of::<ReorderedEnum2>(), 8);
assert_eq!(size_of::<EnumEmpty>(), 0);
assert_eq!(size_of::<EnumSingle1>(), 0);